How to solve my skin showing in my walk animation?
You could remove this part of your mesh, but you could also use the Mask modifier:


Select the part of the skin mesh you want to make invisible, create a vertex group.
Give your skin object a Mask modifier, select the group.
Invert the selection with the double arrows button.
Now this part of your mesh is invisible.




For more complexe meshes you should check out the Mesh Deform modifier method: create a cage around the clothes, give your clothes a Mesh Deform modifier with this cage as Target, and instead of parenting the clothes to the armature, parent the cage...